The development of well defined catalysts with good functional group tolerance has established olefin metathesis as a powerful tool for the formation of carbon-carbon double bonds. See Grubbs, R. H. Handbook of Metathesis; Wiley-VCH: Weinheim, Germany, 2003. Substitution of a phosphine for an N-heterocyclic carbene ligand, in ruthenium-based metathesis catalysts, led to more efficient complexes that maintain the high functional group tolerance and air and moisture stability of the phosphine-containing complexes. See for example, Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R. H. Angew. Chem., Int. Ed. Engl. 1995, 34, 2039-2041; Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1996, 118, 100-110; or Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999, 1, 953-956.
Nevertheless, the development of catalysts that could efficiently control E/Z selectivity in cross-metathesis reactions, or afford tetrasubstituted double bond products in ring-closing metathesis reactions, still represents a major challenge. Furthermore, catalysts more stable toward decomposition are always highly desired.
Thus, what is needed in the art is a catalyst that can accomplish these goals. This invention answers that need.